Tandem mass spectrometry of intact oxidation products of diacylphosphatidylcholines: evidence for the occurrence of the oxidation of the phosphocholine head and differentiation of isomers

• Published in: Journal of mass spectrometry. 2004-12, Vol.39 (12), p.1513-1522
• Main Authors: Reis, A., Domingues, P., Ferrer-Correia, A. J. V., Domingues, M. R. M.
• Format: Article
• Language: English
• Subjects: Analytical, structural and metabolic biochemistry; Biological and medical sciences; Chemistry; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Glycerolipids, phospholipids; hydroxyl radical; Isomerism; Lipids; Mass spectrometry; Organic chemistry; Other biological molecules; Oxidation-Reduction; peroxidation products; phosphatidylcholines; Phosphatidylcholines - chemistry; Reactivity and mechanisms; Spectrometry, Mass, Electrospray Ionization - methods; Structure-Activity Relationship; tandem mass spectrometry
• ISSN: 1076-5174; 1096-9888
• DOI: 10.1002/jms.751

Three glycerophosphatidylcholine (GPC) phospholipids (oleoyl‐, linoleoyl‐ and arachidonoylpalmitoylphosphatidylcholine) were oxidized under Fenton reaction conditions (H2O2 and Fe2+), and the long‐chain oxidation products were detected by electrospray mass spectrometry (ES‐MS) and characterized by ES‐MS/MS. The intact oxidation products resulted from the insertion of oxygen atoms into the phospholipid structure. The tandem mass spectra of the [MNa]+ molecular ion showed, apart from the characteristic fragments of GPC, fragment ions resulting from neutral losses from [MNa]+, and combined with loss of 59 and 183 Da from [MNa]+. These ions resulted from cleavage of the bond near the hydroxy group by a charge‐remote fragmentation mechanism, allowing its location to be pinpointed. The fragments thus formed reflected the positions of the double bonds and of the derivatives along the unsaturated fatty acid chain, giving very useful information, as they allowed the presence of structural isomers and positional isomers to be established. The identification of the fragment ion at m/z 163, which is 16 Da higher than the five‐membered cyclophosphane ion (m/z 147), in some tandem mass spectra, is consistent with the oxidation of the phosphocholine head. Some ions were found to occur with the same m/z value; in two of the phospholipids and based on the MS/MS data, structural and positional isomers were differentiated. Our findings indicate that MS/MS is a valuable tool for the identification of the wide complexity of structural features occurring in oxidized phosphatidylcholines during lipid peroxidation in cellular membranes. Copyright © 2004 John Wiley & Sons, Ltd.